170 POLYTROPA. 



specimens with from one to eight ribs, and' in some of which the 

 ribs become obsolete and replaced by deep striae ; even the shoul- 

 der of the whorls disappears in other specimens, and then we 

 have the form the young of which is described by Krauss as P. 

 cribrosa (fig. 111). The normal development of ribs strikingly 

 resembles the fossil Rapaim (Ecphora) quadricostata, Say, of the 

 United States. 



P. SUCCINCTA, Martyn. PI. 51, figs. 118-120, 107, 125, 113. 



Shell white, encircled 'by about eight strong revolving ribs, the 

 sides of which are deeply excavated ; crossed by rugose growth - 

 lines. Sometimes the interstices of the ribs are filled with ele- 

 vated revolving striue, and occasionally the tops of the ribs are 

 incisely striate. The whole ornamentation is sometimes obsolete. 



Length, 1*5-3 inches. 



Australia ; New Zealand ; Cape of Good Hope, 



This is a more gibbose species than P. cingulata, varieties of 

 which it somewhat resembles ; the clathrate appearance of its 

 initial whorls is a distinguishing character. Its metropolis ap 

 pears to be South Australia, where it is common on rocks, at low 

 water. Sometimes the clath rated growth continues beyond the 

 early whorls, and in this state the shell has received the name of 

 P. squamosa, Lam. (tig. 1 13). This name may be retained as a 

 variety, from Abyssinia and Cape of Good Hope. 



Subgenus Polytropa, Swains. 



P. SCOBINA, Quoy. PI. 51, figs. 123, 112, 121, 122, 124; PI. 52, 

 figs. 126-130, 132, 133. 



Shell very variable, ranging from quite smooth to cancellate ; 

 sometimes with revolving costae, which are occasionally tubercu- 

 late. Color whitish, more or less tinged or flamed with choco- 

 late, brown or yellow. Aperture narrow or wide ; sometimes in 

 the narrower forms obsoletely toothed within the outer lip ; deep 

 chocolate or violet within. Length, '75-1*5 inches. 



New Zealand ; Cape of Good Hope. 



Large, smooth specimens of this mollusk are referred by Kiister 

 to P. versicolor of Gmelin, which would have priority if it could 

 be made out with certainty ; but the figure in Martini referred to 

 by Gmelin is very unsatisfactory. Besides the type, I figure a 



